From eda8b6c7e3ec00c36c6e7d427c498f1dd0a95107 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Collonval?=
 <fcollonval@users.noreply.github.com>
Date: Wed, 2 Aug 2023 18:21:08 +0200
Subject: [PATCH] Backport PR #14865: In defer mode render enough cells to fill
 the viewport

---
 packages/notebook/src/widget.ts | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/packages/notebook/src/widget.ts b/packages/notebook/src/widget.ts
index 7ca076bbc8cc..d04e2f103a41 100644
--- a/packages/notebook/src/widget.ts
+++ b/packages/notebook/src/widget.ts
@@ -887,8 +887,19 @@ export class StaticNotebook extends WindowedList {
       cellIdx++;
     }
 
+    // If the notebook is not fully rendered
     if (cellIdx < this.cellsArray.length) {
-      this._scheduleCellRenderOnIdle();
+      // If we are defering the cell rendering and the rendered cells do
+      // not fill the viewport yet
+      if (
+        this.notebookConfig.windowingMode === 'defer' &&
+        this.viewportNode.clientHeight < this.node.clientHeight
+      ) {
+        // Spend more time rendering cells to fill the viewport
+        await this._runOnIdleTime();
+      } else {
+        this._scheduleCellRenderOnIdle();
+      }
     } else {
       if (this._idleCallBack) {
         window.cancelIdleCallback(this._idleCallBack);